A phosphorylcholine group-containing polymer has excellent biocompatibility typified by blood compatibility. Accordingly, the phosphorylcholine group-containing polymer has been utilized in an application where a coating of the polymer is formed on the surface of a substrate poor in biocompatibility to make the surface biocompatible. Specifically, the polymer has been applied to surface treatment agents for various medical devices, such as an artificial heart, an artificial lung, an artificial vessel, and a contact lens (Non Patent Literature 1).
In such application, the polymer is often used as described below. The polymer is bonded to the substrate surface to which biocompatibility is to be imparted by physical bonding or chemical bonding to form a hydrous coating gel on the substrate surface. In order to perform the physical bonding on the substrate surface, for example, a method involving introducing a comonomer having a hydrophobic group into the polymer having a phosphorylcholine group to perform the physical bonding, or a method involving introducing an ionic group into the polymer to perform ionic bonding is used.
In each of those methods, however, part of the structure of the polymer needs to be substituted with another functional group, and hence the function of a phosphorylcholine group cannot be sufficiently exhibited. Further, when an affinity between the polymer and the substrate is insufficient, the durability of the coating becomes insufficient and hence the coating peels. Meanwhile, a phosphorylcholine group-containing polymer having introduced thereinto a chemical bonding group is chemically bonded to the substrate surface. Accordingly, even when the number of functional groups to be introduced is small, the polymer is bonded to the substrate and hence a coating having relatively high durability can be formed (Patent Literature 1). In this case, however, the presence of a functional group on the substrate surface is an indispensable condition. In addition, in general, bonding between molecules of the phosphorylcholine group-containing polymer does not occur, and hence the durability has not been sufficient. Further, the step of inactivating an unreacted functional group at the time of the chemical bonding through a posttreatment is also required, and hence the phosphorylcholine group-containing polymer having introduced thereinto a chemical bonding group has involved many problems in practical use.
In view of the foregoing, a phosphorylcholine group-containing polymer having photoreactivity has been proposed (Patent Literature 2). Even when a substrate having no chemical bonding functional group on its surface is selected, the polymer can be bonded to the surface of the substrate. In addition, the polymer is excellent in coating formability. However, the polymer has an azido group, and hence sufficient management is needed to secure safety at the time of its production and at the time of its transportation, and stability after the production. Therefore, the polymer has involved problems in terms of supply stability and scale-up property to be solved before its provision to the market.
Sufficient pursuits have not been made on a polymer that has a photoreactive group to be bonded to a substrate surface to be made biocompatible and that is used for forming, on the substrate surface to be made biocompatible, a stable crosslinked body for covering the substrate surface, and a crosslinked body thereof.